1. Brief Description of the Invention
The invention described herein involves improved thickening compositions often referred to as Theological additives, viscosity modifiers or thixotropes, used to impart rheological and viscosity modification properties to a wide range of oil and organic based systems used as paints and coatings. In many commercial applications, such a thickening Theological chemical is added to an oil or organic based paint or coating system, for example epoxy paint, to change or modify the rheological properties of the system. The invention also includes paints and coatings containing such additives.
In an important aspect the invention covers a Theological additive consisting of the reaction product of:                a) a diamine selected from the group consisting of ethylene diamine and hexamethylene diamine;        b) one or more straight chain monocarboxylic acids having 4 to 8 carbon atoms; and        c) 12-hydroxystearic acid.        
The invention is based on a discovery that certain castor based rheological additives, while imparting desirable rheology, impair recoatability and intercoat adhesion of the system in which they are utilized where such systems, after driving, is painted or coated over with a second paint or coating composition. The present invention shows that these undesirable side effects can be avoided by using the inventive additives.
Normally Theological additives should show no reactivity, so they do not react with any other ingredients in the systems in which they are used. Intercoat adhesion is defined as adhesion between adjacent layers of paint when more than one coat of paint or coating is applied to a substrate. Examples of such use are primer and topcoats in home painting and a series of paint coatings applied to automobiles and appliances.
We have concluded it is essential when using additives to structure their chemistry so that, at necessary dosage, they do not adversely affect paint and coating compositions used by customers in systems where more than one coat will be applied to a substrate.
2. Description of the Prior Art
It has been known in the art for many years to use various materials as rheological additives to, among other Theological properties, modify the viscosity of organic systems. Such systems can include paints and coatings, inks, construction materials and wood stains. Depending on the composition of the system, the products made with these thickeners are preferably useful as coatings and paints.
The present invention includes novel rheological additives as well as organic fluid composition containing such additives.
Rheology is defined as the science of the flow and deformation of matter. Rheological additives can be defined as substances added to liquid systems which change that system's flow and viscosity properties. Proper rheology for storage and application must be balanced with the requirement of many fluid systems to resist sagging and dripping during and following application. The term “thixotropy” describes a type of flow behavior in which a temporary reduction in a fluid's viscosity by the application of shear, such as through the use of a paintbrush or atomizing equipment; once the shear forces have been removed, such as following deposition of the liquid onto a surface), the system will regain its initial, higher viscosity.
For background, Japanese Patent Application No. 62-69957 describes a sag preventor for non-aqueous coating materials comprising a mixture of two different fatty acid amides wherein fatty acid amide (A) is obtained by reacting a mixture of at least one straight chain saturated fatty acid having 3-4 carbon atoms and 12-hydroxystearic acid (the molar ratio of the fatty acid and 12-hydroxystearic acid being 1:9-8:1) and ethylene diamine or hexamethylene diamine and fatty acid amide (B) is obtained by reacting a mixture of at least one straight chain saturated fatty acid having 6-22 carbon atoms and 12-hydroxystearic acid (the molar ratio of the fatty acid and 12-hydroxystearic acid being 0:10-8:2) and ethylene diamine, hexamethylene diamine, or xylyiene diamine wherein the weight ratio of fatty acid amide (A) to fatty acid amide (B) is 100:00-20:80.
Products believed to be the reaction product of ethylene diamine, a monocarboxylic acid having ten carbon atoms and 12-hydroxystearic acid have been sold for many years as Theological additives. A product, designated comparative X, using this chemistry has been used as a comparative example to the invention hereof in the below following examples.